If you don’t have the Peterson’s Bird Guide app, get it. It’s often on sale for a buck and is worth every dime. Then look for Nelson’s Sharp-Tailed Sparrow and play the audio clip to hear it “sing.”
The first time I saw one of these critters was in the nearby marsh last summer. It hopped up onto the top of a clump of grass, opened its mouth … then hissed. It was early in the morning and I thought that perhaps I had not had enough coffee. But then another one hopped up on a nearby clump of grass and hissed back. Very unexpected. We live on an interesting planet.